An obligate commensal with Upogebia pugettensis in most or all areas¹ of the west coast is the phoronid Phoronis pallida.  The phoronids live as adults in cemented-sand tubes embedded in the burrow wall (photo on Right), which itself is constructed of sediments bound in mucus (in addition to its binding properties, the mucus acts as a lubricant for the shrimp’s movements; the mucus is secreted from special glands in the hindgut area of the shrimp). The phoronid shown in the photo on the Left occupies the comma-shaped sand-tube originating at the 6-o'clock position. Its feeding apparatus, known as a lophophore, is fully extended.

The author's studies show that competent actinotroch larvae of Phoronis modify their behaviour in the presence of Upogebia-conditioned seawater² such that swimming rates increase significantly (approximately 3-fold) in both downwards and horizontal directions. Once at the sea bottom the larvae probe the sediments with their sensory oral hoods.  The author’s experiments further indicate that ammonia released in urinary excretions from Upogebia is not involved; rather, the chemical cue³ appears to be present in the gut egestia. Also effective at cueing the behaviour are seawater extracts of Upogebia gut tissue and burrow walls. The graph at the lower Right illustrates the dosage-dependency of the response. Santagata 2004 Biol Bull 207: 103.

NOTE¹ collections are made in Bodega Bay, California, Coos Bay, Oregon, and False Bay, Washington

NOTE² 2 liters of seawater in which 2 adult shrimps have been sitting for 2h (at 15^oC). "Dose" in the graph represents µl of Upogegia-conditioned seawater ^. ml^-1 fresh seawater

NOTE³  isolation of the substance from Upogegia-conditioned seawater indicates a molecular size of 10-50 kDa.  Its activity is eliminated by treatment with arginase and significantly reduced by treatment with lipase, suggesting a peptide/fatty acid chemical composition

Transport of species from one region to another as live bait for recreational fisheries invariably runs the risk of escapees surviving to interbreed with the local population.  To assess whether this occurs with ghost shrimps Neotrypaea californiensis being shipped to bait shops in southern California from Oregon and Washington, researchers at California State University, Long Beach analyse 2 mitochondrial DNA markers in populations ranging from False Bay, San Juan Islands, Washington to San Diego, California.  Results reveal nonsignificant genetic structure across the range sampled, suggesting a low risk of genetic homogenisation from interbreeding.  However, the researchers additionally present evidence of a second putative species of Neotrypaea in southern California whose northern range limit is Pt. Conception (see Clade A in diagram), a finding they suggest that is deserving of further reseach.  Finally, and germane to this section on shrimp parasites, they note that about 6% of N. californiensis purchased in bait shops are infected with the host-castrating bopyrid isopod Ione cornuta, and suggest that this risk also merits further study.  Pernet et al. 2008 Mar Biol 153: 1127.

NOTE  genes analysed are fragments of mitochondrial cytochrome b and cytochrome oxidase I

NOTE  samples are from 2 baitshops in Los Angeles County and Orange County, and from 5 field locations north of Pt. Conception and 7 south of Pt. Conception

Distribution of 2 clades of ghost shrimps Neotrypaea
californiensis along the west coast. Shrimps sampled from
2 bait shops in Los Angeles County and Orange County
were originally collected in Oregon and Washington

Large mud shrimps Upogebia pugettensis in Yaquina Bay, Oregon are almost 100% infested with bopyrid¹ isopods Orthione griffenis (see histograms on Right).  Note that the parasites do not infect shrimps less than about 11mm carapace length.  The isopods live in the branchial chambers attached to the gills.  Researchers at the Hatfield Marine Science Center in Newport, Oregon are able to correlate mass² loss in the shrimps with the mass of parasites they carry.  All bopyrid isopods, including Orthione, are obligate blood-parasites that feed on the host’s hemolymph and thus cause loss in mass of the host proportional to the parasite’s energetic requirements³. The authors' results show an average weight loss of 8% owing to the presence of the parasites, but the data are quite variable.  An additional negative effect of a bopyrid parasite is that it often castrates its (male?) host, thus reducing the host’s fitness to zero but without killing it.  However, this effect does not seem to be present in the Yaquina shrimp population.  Smith et al. 2008 J Crust Biol 28: 228. Photograph courtesy USDA Agricultural Research Service.

NOTE¹ world species of thalassinidean decapods in the genera Upogebia and Neotrypaea are commonly infested with bopyrid isopods.  Upogebia spp. alone are known to harbour at least 29 species of the parasite.  Markham 2005 Proc Biol Soc Washington 118: 84

NOTE²  about 1-2% of the shrimps also have parasitic clams Neaeromyra rugifera attached to their pleopods, and these may impose an additional  “parasitic cost”, for example, interference with ventilation and brood carrying.  This might be something worth further investigation

NOTE³  reproductive-energy requirements in Orthione are huge.  A single brood represents about 40% of a female’s mass and is made up, on average, of about 40,000 eggs

Mud shrimp Upogebia pugettensis with parasitic isopod Orthione griffensis removed. Note that the shrimp also has parasitic clams attached to its pleopods 1.6X

Later work at the Oregon Institute of Marine Biology on bopyrid isopods Orthione griffenis parasitic on host thalassinid shrimps Upogebia pugettensis, shows that the isopod originates in China and was likely introduced to the west coast as larvae released in ballast water.  Records of the species in China pre-date the first records of its presence on the west coast by at least 20yr.  In North America Orthione infests mud shrimps U. pugettensis from British Columbia to Point Conception, California.  South of the Point it switches to a replacement mud-shrimp species U. macginitieorum.  The isopod inhabits the branchial chamber of its host and, in addition to possible effects on gas exhange, it may reduce fecundity of female hosts of up to 100%.  Infestation of shrimps may reach 65% in Oregon populations.  The authors provide the first evidence that specimens of Orthione from Asia and North America are the same species.  Williams & An 2009 Integr Comp Biol 49: 1; for a comparison of O. griffenis on both sides of the Pacific see Williams & An 2009 Integr Comp Biol 49: 114.  Photograph courtesy Jason Williams, Hofstra University, New York and Oxford University Press, U.K.

Mud shrimp Upogebia pugettensis with a female bopyrid
isopod Orthione griffenis in its branchial chamber 2X

The bopyrid-isopod parasite Orthione griffensis was introduced to the west coast from Asia sometime in the 1980s.  Two decades later, in 2002, the mud-shrimp Upogebia pugettensis population in Willapa Bay, Washington suffered a huge decline in numbers (see graph), and the question arises as to whether the two events are related. Researchers based primarily at the Hatfield Marine Science Center, Oregon provide strong correlative evidence from 20yr of data that this is indeed the case.  First, levels of infestation of mud shrimps by Orthione are almost non-existent in Willapa Bay during 1988-97 (<1%), but by 1998-2002 are significantly greater, both in males (5-8%) and in females, notably in the 2yr primary-breeder age-class (30%).  Second, the increase in some portions of the Willappa Bay population is exponential from about 1997.  Although causing blood loss and castration (in both sexes), bopyrids do not necessarily kill their hosts.   Fecundity, however, my be significantly decreased, as shown by 68% reproductive losses seen in mud-shrimp populations in Yaquina Bay, Oregon between 2005-09.  Although not assessed specifically, the researchers perforce assume that the levels of parasitism seen in Willapa Bay must have affected both recruitment and population dynamics of the mud shrimps. Dumbauld et al. 2011 Estuaries & Coasts 34: 336.

NOTE  a former west-coast researcher now at the University of South Carolina, Columbia, has earlier used simulation modeling to explore potential mechanisms for causal links between the invasive parasite and decline of its host.  The author’s overall conclusion is that the parasite interferes with its host’s reproduction by increasing the host’s metabolic requirements.  Several hypotheses, all testable, are generated by the models.  These are: 1) infection should be proportional to degree of exposure to parasite-laden water, and this will vary with tidal height and pumping rate of the shrimp, 2) the metabolic burden will be proportional to parasite size, 3) the greater the metabolic imposition, the greater will be the degree of feminisation of male hosts, and 4) metabolic costs of infection will be most severe in higher intertidal regions, where feeding time is most restricted.  The author concludes by stating that, if tested, these hypotheses will greatly contribute to our understanding of  the interactive dynamics of Upogebia and Orthione.  Griffen 2009 Mar Ecol Progr Ser 391: 73.